1. Field of the Invention
The present invention relates to a photopolymerizable or radiation polymerizable resin composition which can be developed by means of alkaline solution.
2. Description of the Related Art
In recent years, a so-called dry film resist, consisting of a photopolymerizable resin layer sandwiched between a supporting film layer and a protective film layer, has come into widespread use as a photo-resist used in the manufacture of printed circuit boards. As the photopolymerizable resin layer, solvent developing resins, in which portions unexposed to light are removable by treatment with a chloro-organic solvent, and alkaline developing resins, in which unexposed portions thereof are removable by treatment with an alkaline aqueous solution, are known. However, due to environmental as well as manufacturing cost considerations, alkaline developing dry film resists have come to be the most widely employed.
The method of use for the alkaline developing dry film resist possessing a supporting film layer and a protective film layer consists of the following. First, while stripping away the protective film layer from the dry film resist, the surface of the photopolymerizable resin layer is heat laminated onto a copper foil laminated sheet. Following this, a photo-tool is brought into tight contact with the surface of the supporting film of the film resist, after which exposure curing of the parts to be cured is performed with ultraviolet rays and the like. After the supporting film is peeled away, development proceeds with the removal of unexposed portions by means of weak alkali aqueous solutions such as sodium carbonate, producing a resist circuit pattern. Following this, in the case of the copper through-hole procedure, after carrying out etching of the copper surface, the cured resist is peeled a way using a strong alkali aqueous solution such as sodium hydroxide, producing a printed circuit board. Additionally, in the case of the solder through-hole procedure, after performing copper and solder plating, the cured resist is stripped using a strong alkali aqueous solution, and the exposed copper is further etched, producing the printed circuit board.
When comparing the solder through-hole procedure to the copper through-hole procedure, the thickness of the copper removed after etching is thin, and as a result, there is little thinning of the copper pattern by unnecessary side etching, making this procedure appropriate for the manufacturing of fine patterns.
When forming a circuit pattern using the solder through-hole procedure, it is essential that the dry film resist possess a sufficient resistance as a plating resist. However, with most of the conventional alkaline developing dry films, the cured resist peels off during copper or solder plating, and plating fluid soaks in between the cured resist and the copper surface. Accordingly, frequent incidence of the so-called "submerged plating" phenomenon in which portions outside of the circuit portion are also plated, as well as a number of other problems such as short-circuiting of the conductor, enlargement of the conductor width and disruption of the shape of the conductor periphery portion also occur.
As a result, various investigations have been carried out in order to improve the antiplating properties. However, in most of the alkaline developing dry film resists with improved antiplating properties, improving the chemical resistance of the composition was established as the main goal in order to increase the antiplating properties, and as a result, although the cured resist was stripped by a strong alkaline aqueous solution, a drawback existed in that a long time (stripping time) was required for this operation. If the stripping time is long, the time required for manufacturing the circuit pattern becomes longer, and not only is there no increase in productivity, but also the copper surface of the substrate is oxidized by the alkali and discolored and is further detrimentally affected in the etching process. Optionally, the solder was dissolved by means of immersion for an extended period of time in a strong alkaline aqueous solution, giving rise, during the etching process, to thinning of the pattern and disconnection, as well as elimination of fading.
Most of the conventional alkaline developing dry film resists possessing a short stripping time not only have insufficient antiplating properties, but are also disadvantageous in that the stripped plate of the cured resist, stripped by means of a stripping fluid with strong alkali properties is easily dissolved in the same stripping fluid. If the stripped plate of the cured resist is easily dissolved in the stripping fluid, this stripped plate, during retention in the stripping tank, swells easily, acquiring a gel-like form. This gel-like substance then sticks to the stripped plate, resulting in clogging of the filter provided in the stripping machine. This in turn results in reduction of the circulation amount of the stripping fluid, and hence stripping of the cured resist becomes impossible, and also results in overflow of the stripping fluid from the stripping tank, and contamination of the periphery of the tank.